1. Field of the Invention
The present invention relates to a wafer holder for a semiconductor manufacturing apparatus and to a method of manufacturing the wafer holder. Examples of the holder include a holder which has at least one of a heater serving a function of heating a semiconductor wafer from below, an electrostatic chuck electrode used for generating an electrostatic force between the electrode and a semiconductor wafer in order to secure the wafer, and a plasma lower electrode used for generating plasma.
2. Description of the Background Art
For etching of a semiconductor wafer surface or depositing of a film thereon, a method has been employed according to which gas for etching or for film deposition is supplied by means of a batch processing system to a large number of wafers held on racks, and then the wafers are heated as required from the outer periphery (hot wall method).
However, as requirements become severer for higher integration and speed of semiconductor devices, a problem arises of non-uniform etching and unequal quality of completed films due to difference in temperature and gas flow depending on the location in a semiconductor manufacturing apparatus. Then, another type of semiconductor manufacturing apparatus has gradually been used instead that employs a single wafer processing system in which a plurality of etching apparatuses and film deposition apparatuses are arranged side by side and wafers are transported automatically by a loader through the apparatuses where the wafers are processed one by one. In a semiconductor manufacturing apparatus of such a single wafer processing type, a method is employed according to which the loader transports the wafer onto a wafer holder in a chamber of an etching apparatus or film deposition apparatus, the wafer is secured to the holder by an electrostatic chuck or statically fastened to the holder by enhancing surface precision of a wafer-supporting surface of the holder, and then heat is directly applied to the holder to uniformly heat the wafer. It is thus necessary that at least the portion of the holder, which is in contact with the wafer, is formed of a material having corrosion resistance against a highly corrosive gas such as halogen gas and the like and having a high heat conductivity, and that the holder itself has an electrostatic chuck function and a mechanically fixing function, as well as a heater function.
Aluminum nitride has been attracting attention as a material for the holder because of its corrosion resistance and high heat conductivity. The holder has been produced by providing a coil or wire of refractory metal such as molybdenum and the like between compact pieces formed of aluminum nitride powder and hot-press sintering them so as to produce a conductive layer, as a heater or electrostatic chuck electrode, embedded in the holder. Regarding a holder having a heater embedded therein, Japanese Patent No. 2604944, for example, discloses a heater-embedded structure for enhancing uniformity of heating on a heat-generating surface. A method has been employed for producing a holder having a conductive layer embedded between stacked compact pieces. According to this method, paste containing tungsten or molybdenum is printed on a surface of an aluminum nitride compact piece, such compact pieces are stacked, and the aluminum nitride compact pieces and the paste are sintered simultaneously.
However, the above method, according to which coil or wire of refractory metal such as molybdenum is provided between aluminum nitride compact pieces and then they are hot-press sintered, has a problem that the coil or wire mounted on the compact piece is displaced from its original position through a handling process before the subsequent hot-press sintering process, resulting in products having respective characteristics considerably different from each other, as well as short-circuit. In order to avoid this, a method is employed by which grooves are made in a compact piece to insert a coil or wire into the grooves. In this case, the precision of a conductor pattern for generating a heater or electrostatic chuck electrode is governed by the pattern precision of grooves formed in a compact piece. However, it is difficult to form grooves having a fine pattern in an aluminum nitride compact piece. If grooves having a width and an interval of 5 mm or less are formed in the compact piece, a thin wall between the grooves is likely to be partially lost. In terms of mass production, the grooves should be formed at intervals of at least 10 mm. Therefore, it has been difficult to produce a conductor for a heater or electrostatic chuck electrode with a fine and highly precise pattern by forming grooves in a compact piece.
Another problem is that production of a large-sized sintered aluminum nitride piece by the hot-press sintering method as discussed above requires a large-sized apparatus which raises equipment cost and accordingly increases manufacturing cost.
In addition, when paste of refractory metal such as tungsten is printed on an aluminum nitride compact piece and then another compact piece is layered thereon to simultaneously sinter the aluminum nitride compact pieces and the metal paste, difference in density between the compact pieces and non-uniform heating cause shrinkage resulting from the sintering to vary depending on location or product. Then, it is difficult to produce a conductive layer with a high precision pattern. According to another method employed, surfaces of compact pieces are wetted with a solvent, and then the compact pieces are stacked, heated, and pressure-bonded and thereafter degreased and sintered. In the heating process, the pressure-bonded portion is subject to partial or entire peeling and thus production is difficult to achieve through stable processes.
If a holder is manufactured through the simultaneous sintering as discussed above, high-precision control of shrinkage in the sintering is difficult. The possibility of peeling of the bonded portion makes it difficult to enhance manufacture yield, resulting in increase in manufacturing cost.
Any of the methods above employs simultaneous sintering of the aluminum nitride compact pieces and coil or wire of refractory metal or metal paste. Therefore, material for the conductive layer is limited to refractory metal such as tungsten and molybdenum. Then, silver-palladium alloy and the like having a low melting point cannot be used as a material for the conductive layer. A problem here is that the range of controlling an amount of generated heat is restricted when such a conductive layer is used as a heater.
Ceramic such as aluminum nitride used as a material for a holder is advantageously fabricated to have a high heat conductivity in order to allow a resultant holder to uniformly heat a semiconductor wafer held thereon. However, the ceramic like the aluminum nitride should be sintered at high temperature for a long period of time in order to enable the sintered ceramic to have a high conductivity. If a ceramic compact piece is sintered at high temperature for a long period of time, abnormal grain growth could occur in tungsten or molybdenum used as a material for a conductor, or an agent used for sintering aluminum nitride and the like could excessively react with an agent added for firing metal paste of tungsten or molybdenum to cause breaking of the conductive layer or defect in bonding. For this reason, the compact piece of ceramic such as aluminum nitride should be sintered at a low temperature of 1800xc2x0 C. or less for a short period of time. Consequently, the ceramic such as aluminum nitride cannot be sintered to have a high heat conductivity and a resultant holder cannot provide uniform heating. There is thus a limit to manufacturing of a holder capable of heating a wafer uniformly.
One object of the present invention is accordingly to provide a wafer holder for a semiconductor manufacturing apparatus that can overcome the above problems, can be manufactured to have a high heat conductivity, and enables a conductive layer to be embedded therein with a high precision pattern, and to provide a method of manufacturing such wafer holder and a semiconductor manufacturing apparatus having therein the wafer holder.
Another object of the invention is to provide a wafer holder for a semiconductor manufacturing apparatus that can be manufactured at a high manufacture yield rate and a low cost, a method of manufacturing such wafer holder, and a semiconductor manufacturing apparatus having therein the wafer holder.
According to the present invention, a method of manufacturing a wafer holder for a semiconductor manufacturing apparatus that has the structure described in (1) or (2) below includes the following steps.
(1) A method of manufacturing a wafer holder having a xe2x80x9cceramic/joint layer/conductive layer/ceramicxe2x80x9d structure includes the steps of:
a. applying paste containing metal particles onto a surface of a first sintered ceramic piece and firing the paste to form a conductive layer; and
b. joining the first sintered ceramic piece and a second sintered ceramic pieces by providing a joint layer between the surface of the first sintered ceramic piece having the conductive layer formed thereon and the second sintered ceramic piece and heating them.
(2) A method of manufacturing a wafer holder having a xe2x80x9cprotective layer/conductive layer/ceramicxe2x80x9d structure includes the steps of:
a. applying paste containing metal particles onto one or both of the surfaces of a sintered ceramic piece and firing the paste to form a conductive layer; and
b. forming a protective layer on the sintered ceramic piece to cover a surface of the conductive layer.
According to the method of manufacturing the structure described in (1), the sintered ceramic pieces are joined. Therefore, if respective warps of the first and second sintered pieces do not conform to each other or any load or the like is insufficient in the joint process, some defect such as gap in joint could occur, which could lead to decrease in yield. In terms of yield and cost, the method of manufacturing the structure described in (2) is preferred according to which the conductive layer is formed on one side of one sintered piece and the surface of the conductive layer is covered with the layer protecting the surface from corrosive gas such as halogen. In this case, on one side or both sides of the sintered piece can be provided with an electrode or electrodes formed thereon, therefore, a holder can be fabricated to have selected one or two of a heater circuit, a plasma lower electrode and an electrostatic chuck electrode. After the protective layer is formed, the surface of the protective layer can be processed mechanically or chemically, or processed mechanically and chemically in combination, according to requirements of surface roughness and flatness of the surface of the protective layer.
According to the manufacturing methods of (1) and (2), the conductive layer is formed by applying paste containing metal particles onto the surface of the ceramic piece which is preliminarily sintered and firing the paste. The sintered ceramic piece is prepared in advance through the sintering process before the paste containing metal particles is applied such that the sintered ceramic piece has a high heat conductivity. Therefore, the sintered ceramic piece can be prepared to have a high heat conductivity as a material for the holder through the sintering at high temperature over a long period of time.
Further, on the surface of the sintered ceramic piece prepared in advance, the paste containing metal particles can be applied to form a pattern with a high precision considering heat balance and the like and then fired. The firing temperature for the metal particles is lower than the sintering temperature for the sintered ceramic piece. Therefore, the sintered ceramic piece as a base does not shrink, and accordingly the conductive layer with high precision can be formed on the surface of the sintered ceramic piece while keeping the pattern precision of the paste as applied.
Although the surface of the wafer holder on which a wafer is placed can be polished to remove any warp of the surface, warp or undulation of the conductive layer in the wafer holder remains unchanged. Consequently, the wafer on the wafer holder has its temperature varied due to the influence of warp or undulation of the joined sintered pieces or the sintered piece having the protective layer formed thereon that has not been polished. Different from the conductive layer formed by applying paste containing metal particles on the surface of the compact piece and simultaneously sintering the paste and compact piece, the conductive layer according to the present invention is produced by applying paste containing metal particles on the surface of the sintered piece and firing the paste. The sintered piece hardly deforms compared with the compact piece. For this reason, warp of the sintered ceramic piece occurring due to shrinkage in the firing process of the paste can be made small and then the wafer can be heated uniformly.
Further, it is easy to increase the amount of heat as designed that is generated, for example, from the periphery which is likely to decrease in temperature due to radiation and the like or from the joint with the protective part for the power lead line which is likely to decrease in temperature due to heat transmission. Therefore, the wafer holder can be fabricated that is capable of heating the entire surface of a wafer uniformly.
By reducing the line width and the line interval of the linear pattern of the conductive layer, uniform heating can be achieved which lessens the influence of difference in temperature between the part on the heater wire and the part on the interval between heater wires on the wafer heating surface. In addition, a complicated pattern of the conductive layer can easily be designed.
The temperature distribution of the wafer in a film deposition process should be within 1%. Therefore, preferably, the line width and the line interval of the linear pattern of the conductive layer are each 5 mm or less. If possible, the temperature distribution of the wafer is preferably within 0.5%. In order to achieve this, the line width and the line interval each should be 1 mm or less. According to the manufacturing method of the present invention, by reviewing conditions of applying paste by printing that contains metal particles, the conductive layer can be formed to have the linear pattern with the line width and the line interval each of 5 mm or less. Preferably, it is also possible to form the linear pattern of the conductive layer to have the line width and the line interval each of 1 mm or less.
According to the method of manufacturing a wafer holder for a semiconductor manufacturing apparatus of the present invention, ceramic as a base material for the holder preferably includes any one of aluminum nitride, aluminum oxide, silicon nitride and aluminum oxynitride. Use of such ceramic enables the wafer holder to have heat resistance as well as corrosion resistance against corrosive gas including halogen for example that is used as a reactant gas.
More preferably, according to the method of manufacturing a wafer holder for a semiconductor manufacturing apparatus of the present invention, ceramic used as a base material for the holder is aluminum nitride. Use of the aluminum nitride enables the holder to be manufactured to have a high heat conductivity of at least 100 W/mK and a high corrosion resistance against halogen gas and the like.
According to the manufacturing method of the invention, in the step of forming the conductive layer, preferably the paste containing at least one type of metal selected from the group consisting of tungsten, molybdenum, silver, palladium, platinum, nickel and chromium is applied and fired. In particular, according to the manufacturing method of the invention, the conductive layer is formed on the surface of the sintered ceramic piece which is prepared in advance, therefore, the conductive layer can be formed by applying paste of silver-palladium alloy and the like with a low melting point and firing the paste.
According to the present invention, in the step of joining the first and second sintered ceramic pieces in the manufacturing method of (1) or in the step of forming the protective layer on the sintered ceramic piece in the manufacturing method of (2), organic-based adhesive may be used. However, in terms of heat resistance, preferably a layer containing glass is provided between the sintered pieces or applied onto the sintered piece and then heated in those steps.
By joining the sintered ceramic pieces using the oxide layer such as glass as the joint layer or the protective layer, a fine conductive layer pattern for forming the heater circuit, the electrostatic chuck electrode and the plasma lower electrode can be produced with a desirable yield and at a low cost.
If any one of aluminum nitride, aluminum oxide, silicon nitride and aluminum oxynitride is employed as ceramic for a base material of the holder, the joint layer or the protective layer discussed above is preferably a layer containing glass having a thermal expansion coefficient from 3.0xc3x9710xe2x88x926/xc2x0 C. to 8.0xc3x9710xe2x88x926/xc2x0 C. Desirably the time required to increase the temperature of the wafer holder from room temperature to 600xc2x0 C. is within 30 minutes. If the thermal expansion coefficient of the joint layer or the protective layer is within that range, the temperature can be increased in 30 minutes or less.
By using such a glass layer as the joint layer or the protective layer, the joint layer or the protective layer can be made substantially equal to the sintered ceramic piece in thermal expansion coefficient. Then, thermal stress generated in the step of joining, forming the protective layer, or heating and cooling of the holder can be reduced.
In terms of wetting and bonding properties, if the sintered ceramic piece as a base material is aluminum nitride, the joint layer or the protective layer preferably includes oxide containing ytterbium (Yb), neodymium (Nd) and calcium (Ca) or includes a compound which generates oxide containing ytterbium (Yb), neodymium (Nd) and calcium (Ca) by being heated. In terms of the same properties, if the sintered ceramic piece as a base material is silicon nitride, the joint layer or the protective layer preferably includes oxide containing yttrium (Y) and aluminum (Al) or includes a compound which generates oxide containing yttrium (Y) and aluminum (Al) by being heated.
According to the method of manufacturing a wafer holder which is used at high temperature by being applied with high voltage, in the step of joining in the manufacturing method of (1) or the step of forming the protective layer in the manufacturing method of (2), nonoxide ceramic is more preferably used as a material for the joint layer or the protective layer in terms of heat resistance, corrosion resistance, and voltage resistance.
Preferably, the above nonoxide ceramic has a thermal expansion coefficient in the range of 3.0xc3x9710xe2x88x926/xc2x0 C. to 6.0xc3x9710xe2x88x926/xc2x0 C. for alleviating thermal stress.
Preferably, the above nonoxide ceramic contains at least 50% by weight of aluminum nitride or silicon nitride in terms of heat resistance, corrosion resistance and voltage resistance.
According to one aspect of the invention, a wafer holder for a semiconductor manufacturing apparatus includes a first sintered ceramic piece, a second sintered ceramic piece, a conductive layer formed on a surface of the first sintered ceramic piece, and a joint layer provided between the surface of the first sintered ceramic piece having the conductive layer formed thereon and a second sintered ceramic piece for joining the first and second sintered ceramic pieces.
According to another aspect of the invention, a wafer holder for a semiconductor manufacturing apparatus includes a sintered ceramic piece, a conductive layer formed on one or both of surfaces of the sintered ceramic piece, and a protective layer formed on the sintered ceramic piece to cover a surface of the conductive layer.
For the wafer holder for a semiconductor manufacturing apparatus manufactured according to the present invention, the ceramic preferably includes any one of aluminum nitride, aluminum oxide, silicon nitride and aluminum oxynitride, and more preferably, the ceramic is aluminum nitride.
When film deposition or etching is carried out on a semiconductor wafer by CVD and the like, a film is also deposited on the surface of the wafer holder. Particles generated due to peeling of the film could adhere to the semiconductor wafer. In order to prevent this, the wafer holder should be cleaned after it is used for some time. For example, once a day or once in two or three days, the temperature of the inside of a chamber is decreased for cleaning, or the temperature of the inside of the chamber is decreased to room temperature approximately once per month, and then the chamber is opened for cleaning the wafer holder. After the cleaning, the temperature is desired to be raised from room temperature to a temperature for reaction as immediately as possible. Specifically, it is desired to increase the temperature from room temperature to 700xc2x0 C. within 10 minutes (temperature increase rate is 70xc2x0 C./min or higher), and within 7 minutes (temperature increase rate is 100xc2x0 C./min or higher) if possible. In order to immediately lower or raise the increased or decreased temperature of the wafer holder to a predetermined temperature, it is desired for the wafer holder to have the property of immediately increasing or decreasing in temperature at a rate of 70xc2x0 C./min or higher or 100xc2x0 C./min or higher if possible. In order to meet such requirements, the wafer holder of the present invention preferably has a thickness of 5 mm or less and more preferably has a thickness of 2 mm or less.
For the wafer holder for a semiconductor manufacturing apparatus manufactured according to the present invention, the conductive layer preferably includes a linear pattern of the conductive layer with a line width and a line interval each of 5 mm or less. More preferably, the line width and the line interval each are 1 mm or less.
For the wafer holder for a semiconductor manufacturing apparatus manufactured according to the invention, the conductive layer preferably contains at least one type of metal selected from the group consisting of tungsten, molybdenum, silver, palladium, platinum, nickel and chromium.
It is noted that the conductive layer preferably contains at least 50% by mass of at least one of the above metal materials.
For the wafer holder for a semiconductor manufacturing apparatus fabricated according to the invention, the joint layer or protective layer preferably contains glass.
If any one of aluminum nitride, aluminum oxide, silicon nitride and aluminum oxynitride is employed as ceramic for a base material of the holder, the joint layer or the protective layer mentioned above is preferably a layer containing glass having a thermal expansion coefficient from 3.0xc3x9710xe2x88x926/xc2x0 C. to 8.0xc3x9710xe2x88x926/xc2x0 C.
If the base material is aluminum nitride, the joint layer or the protective layer preferably includes oxide containing ytterbium, neodymium and calcium or includes a compound which generates oxide containing ytterbium, neodymium and calcium by being heated. If the base material is silicon nitride, the joint layer or the protective layer preferably includes oxide containing yttrium and aluminum or includes a compound which generates oxide containing yttrium and aluminum by being heated.
For the wafer holder for a semiconductor manufacturing apparatus fabricated according to the invention, if the holder is used at high temperature by being applied with high voltage, the joint layer or the protective layer preferably contains nonoxide ceramic in terms of heat resistance, corrosion resistance and voltage resistance.
In this case, if the ceramic employed as a base material for the holder is any of aluminum nitride, aluminum oxide, silicon nitride and aluminum oxynitride, the joint layer or the protective layer discussed above is preferably a layer containing nonoxide ceramic having a thermal expansion coefficient in the range of 3.0xc3x9710xe2x88x926/xc2x0 C. to 6.0xc3x9710xe2x88x926/xc2x0 C. The nonoxide ceramic preferably contains at least 50% by weight of aluminum nitride or silicon nitride. More preferably, the protective layer is formed of glass or nonoxide ceramic having aluminum nitride as its main component.
In order to actually use the wafer holder of the present invention in a CVD apparatus or etching apparatus, the wafer holder preferably includes an electrode member connected to the conductive layer and extended to the outside of the wafer holder. In order to prevent the electrode member from being corroded by corrosive gas such as halogen, the electrode member preferably includes a conductive base material and a ceramic layer covering the surface of the base material.
The ceramic layer is preferably formed of aluminum nitride or aluminum oxide in terms of heat resistance and corrosion resistance.
Preferably, the ceramic layer is formed by PVD, CVD or thermal spraying in terms of densification and the like.
Preferably, the base material for the electrode member is formed of tungsten or molybdenum for decreasing difference in thermal expansion coefficient between the base material and the ceramic and accordingly reducing thermal stress and in terms of heat resistance.
A semiconductor manufacturing apparatus according to the present invention includes therein the wafer holder for the semiconductor manufacturing apparatus that is structured as detailed above.
The semiconductor manufacturing apparatus according to the present invention is one selected from the group consisting of etching apparatus, CVD apparatus, plasma CVD apparatus and ion implantation apparatus.
As heretofore described, according to the present invention, it is possible to manufacture a holder, as a wafer holder employed in a semiconductor manufacturing apparatus for film deposition or etching that is required to uniformly heat a semiconductor wafer having a relatively larger outer diameter. The manufactured holder has therein a heating circuit having a fine pattern considering thermal shrinkage and the like, an electrostatic chuck electrode, or a plasma lower electrode with a high precision. Further, the wafer holder can be manufactured with an improved manufacture yield and at a low cost compared with the conventional holders.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.